This invention relates to organic conductors and semiconductors which fall into the group of polymeric pyrrole conductors. As is well known, such conducting polymers defy conventional melt-processing, cannot be compacted, whether molded or extruded, in the usual ways, nor deposited as a continuous film from solution; and, they are far from stable in air even at ambient temperature conditions. A polymer which defies compaction into a shaped article, places severe limitations upon its use. Certain pyrrole polymers made by electrodeposition are found to be compactable (see copending U.S. patent application Ser. No. 486,161, filed Apr. 18, 1983), and to form self-supporting films, but this process is too slow for general commercial utility. The problem was to find a relatively fast non-electrochemical process which yielded a compactable conductor (the term "conductor" as used herein includes semiconductors) so that the polypyrroles formed might be more versatile in their applications.
By "semiconductors" I refer to polymers of pyrrole/substituted pyrrole monomers which have relatively low conductivity in the range from about 10.sup.-3 ohm.sup.-1 cm.sup.-1 ("S/cm" for convenience to indicate reciprocal ohms/cm) to 1 S/cm, while "conductors" have a conductivity in the relatively high range of from 1 to about 150 S/cm.
Poly(2,5-pyrrole) (referred to herein as "PP" for brevity), in which the --NH-- group links sequences of conjugated double bonds, is normally an insulator, that is, has a conductivity less than about 10.sup.-10 S/cm and is totally insoluble in known solvents. It is known however, that electrochemically polymerized PP has good conductivity, but coupled with its melt-processing-resistance and the poor integrity of PP film so formed, it was deemed more desirable to produce the PP with a chemical process. Others have also sought to do so. In particular, German (FDR) Offenlegungasehrift DE 3321281 A1 published Dec. 22, 1983 discloses a chemical process for producing a conductive paper by impregnating the paper with different concentrations of an aqueous ferric chloride solution which is acidified with HCl, then exposing the impregnated paper to pyrrole monomer, usually in the gaseous phase. Further details of this process are disclosed in an article titled "Some Properties of Polypyrrole-Paper Composities" by Bjorklund, R. B. and Lundstroem, I., Journal of Electronic Materials, Vol 13, No. 1, 1984.
As also stated in Bjorklund et al, they were aware that anhydrous FeCl.sub.3 used as a dopant with poly-p-phenylene exists as an FeCl.sub.4 (2.sup.-) complex in the polymer matrix, thus imparting conductivity to the polymer. Other polymers, for example polyacetylene impregnated with FeCl.sub.3 or other oxidants such as SbCl.sub.5, and, neutral polypyrrole which is exposed to FeCl.sub.3 vapor or an anhydrous solution of the electrolyte, is also made conductive. But impregnating a preformed polymer with FeCl.sub.3 to make it conductive does not suggest that one may use anhydrous FeCl.sub.3 as an initiator to form the polymer from the pyrrole monomer, or that the FeCl.sub.3 would generate a charged species in the polymer formed. As is well-known, poly-p-phenylene cannot be formed by initiation with FeCl.sub.3 (see "Reaction of Ferric Chloride with Benzene", by P. Kovacic and C. Wu, J. Polym. Sci. Vol XLVII pg 45-54 at pg 45, first sentence of "Results", 1960), and the polymer is not conductive unless post-treated with FeCl.sub.3.
The insulating character of PP produced by Naarman is attributable to the combination of AlCl.sub.3 and Cu.sup.+2 Cl.sub.2 as the initiator, further possibly to the low molar ratio of the initiator to the pyrrole in the reaction mixture.
With respect to polymers of 3- and/or 4- substituted pyrroles ("subs PP"), Bjorklund et al corroborate the generally well known fact that providing substituents on pyrrole does not improve the conductivity of the subs PP. Yet, with the process of my invention, the designated subs PP has relatively good conductivity.
As noted by Bjorklund et al, their precipitated PP was compactable under 10 ton pressure to form a wafer. PP precipitated in my polymerization reaction is compacted under far less pressure into a wafer which can be handled, but the wafer, unlike wafers or films produced from electrochemically produced PP, has essentially no tensile strength.
The conductive PP/subs PP of the prior art which polymers owe their conductivity to exposure to an electrolyte of a Group VIII metal, for example FeCl.sub.3, whether by exposure to FeCl.sub.3 vapor, or by impregnation with an anhydrous solution of electrolyte, derive their conductivity from a FeCl(2.sup.-) counter ion in which the Fe (or other Group VIII metal) is always present. It was therefore surprising to find that excellent conductivity, as high as 150 S/cm, may be obtained with only Cl present as the counter ion, and without the presence of Fe.
Though it appeared that the type of initiator (electrolyte) would affect the electrical properties of the polymer, the possibility that the solvent might affect the charged species in the polymer was given little consideration. And the possibility that a single initiator could provide different charged species in the same polymer if it is formed under different conditions, was given even less consideration. Thus the formation of PP/subs PP.sup.+ Cl.sup.-1 by a direct, single-step chemical process was both significant and unique.